Which device measures electrical resistance?

• A. Ohmmeter
• B. Ammeter
• C. Voltmeter
• D. Wattmeter

Answer: (A)

Measuring resistance relies on using a device that applies a small stimulus and reads the response so Ohm’s law can be used to calculate R. An ohmmeter injects a known, safe current (or applies a small voltage) through the unknown resistance and measures the resulting voltage (or current). It then computes resistance as R = V / I and displays the value. This is why the instrument designed for resistance measurement is the correct choice.

A device that measures current is an ammeter, a device that measures voltage is a voltmeter, and a device that measures power is a wattmeter. For accurate resistance readings, circuits are usually de-energized and, if possible, the component is isolated from other paths to avoid parallel currents.